The present invention relates to a gas-flow type chipping machine with a rotating beater-wheel system and a method for optimizing such chipping machines.
A consequence of the constantly growing demand for wood chips to be used, for examples in manufacturing chip board, which is being voiced by the wood-processing industry, is that ever larger machines with greater throughput capacities are being built to produce the starting materials that are required to satisfy this demand. Recently, old wood that has been recovered by recycling has been used as the raw material for manufacturing wood chips. These developments are causing various problems that have been overcome with the aid of the present invention.
On the one hand, depending on the purpose for which it was previously used, old wood can contain a comparatively large quantity of impurities. In the case of construction lumber, these impurities are frequently in the form of traces of concrete and sand that have adhered to be wood, as well as nails and screws. DE 43 16 350 describes an effective way of removing such impurities from the feed material. To this end, an input apparatus in the form of a wind sifter is incorporated ahead of a chipping device. The feed material, previously cleaned by a magnetic drum and a sieve surface, is passed through a sifting channel in which relatively heavy particles are separated out. The transverse flow of air that performs the actual sifting also serves as the motive force that moves the feed material through a wide channel into the chipping area of the chipping machine. Chipping machines that are configured in this way achieve a high level of separation of foreign matter and deliver good chip quality, always providing that the material is sufficiently homogeneous with respect to size and density.
This cannot always be assured when old wood is reused, when different types of wood of various densities are mixed so that the chipping knives that extend to the full depth of the chipping area are not acted upon uniformly to their total length. Rather, there are zones in which the more material collects, with the result that more chipping work has to be done. The result is greatly increased localized wear that leads to the need for premature replacement of the blades and thus to shorter machine run times.
This undesirable effect is also exacerbated by the design of powerful machines with deeper chipping areas, in which it is, of course, more difficult to ensure that the length of the blades can be acted upon uniformly because they are so long.
Certainly, DE-OS 224 37 202 and DE-PS 26 01 384 describe measures to ensure that the blades are acted upon in a uniform manner. However, because of the fundamentally different ways of delivering the feed material into the chipping area, these cannot of necessity be transferred to the present invention. In the cases of both OS 24 37 202 and DE-PS 26 01 384, the Reed material passes through an inclined entry chute by gravity, and then enters the chipping area at its centre. In the case of OS 24 37 202, the entry chute is divided into a plurality of tracks that extend to varying distances into the interior of the chipping area. At the end of each track there is an impact plate that diverts the flow of material to the chipping tools into a radial direction. Because of the arrangement of the impact plate, which are staggered to the depth of the chipping area, the material is distributed evenly to the depth of the chipping area.
In the case of DE-OS 26 01 384, at its machine end, the fixed entry chute becomes a rotating truncated cone within which there is a similarly rotating distributing device. The distributing device consists essentially of three circular sectors that are staggered to the depth of the chipping area and are separated by bulkheads; diametrically opposed cutouts in the outer surface of the truncated cone are associated with these circular sectors. The feed material is delivered to specific areas of the chipping tools through the cutouts in the outer surface.
It is true that these known devices that ensure that the chipping tools are acted upon evenly to the whole length function work well in the case of chipping machines with an entry for the material by way of a chute, and if the feed material is homogeneous; however, as a result of design and construction constraints they cannot be used in conjunction with a chipping machine that has a pneumatic charging system that is preferably combined with a previous wind-sifting system. Whereas the entry chute controls the feed material at low speeds and guides it to a predetermined point in the chipping area, in the case of pneumatic charging that is effected with the aid of the flow of air, the feed material is injected into the chipping area at high speed. Measures that belong to the prior art cannot accommodate the feed material that arrives with a great deal of kinetic energy from a predetermined direction, and then deliver it to the chipping tools.
Against this background, it is the objective of the present invention to describe a gas-flow type chipping machine in which the charging is effected pneumatically and in which the chipping tools are acted upon uniformly to their whole length.
According to the present invention, this objective has been achieved by a chipping machine, wherein, in order to ensure that the feed material is evenly distributed to the length of the chipper tools, there are at least two impact surfaces that are arranged in the chipping area so as to be axially staggered by depth, the impact surface that follows in the axial direction of delivery projecting beyond the axial projection of the preceding impact surface.
It is a further objective of the present invention to describe a method for optimizing the position and dimensions of the impact surfaces according to the present invention.
This objective has been achieved by a method with the following steps: a) the wear on the chipping tools at specific positions prior to operation is determined; b) the machine is operated for a specific amount of time; c) the wear on the chipping tools at the places identified in a) is determined; the diameter and/or spacing of the impact surfaces is varied in the event that the wear on the chipping tools is not constant at the locations identified in a); the steps a) to d) are repeated until such time as the wear on the chipping tools is constant at the locations identified in a).
According to the present invention, the feed material is deflected radially on impact surfaces that are arranged at different depths, as a function of the eccentricity of the projections on which the feed material moves into the chipping machine. In this way, a radial material track can be associated with each axial trajectory, each of said tracks leading to one specific sector of the drum-like chipping track. Only by creating conditions that are so defined can the way in which the chipping tools are acted upon to their whole length be controlled by changing parameters such as the position and/or dimensions of the impact surfaces. Because of this it is possible to introduce inhomogeneous material into a chipping machine according to the present invention, or increase the depth of the chipping area in order to increase the throughput rate. Althoughxe2x80x94in the pastxe2x80x94this resulted in great costs because of locally increased wear on the chipping tools, now the chipping tools themselves are worn evenly to their whole lengths under such conditions, so that the interval between tool changes have become longer, and machine run time is correspondingly longer, with the result that overall economy has been enhanced.
The chipping machines according to the present invention are particularly advantageous in the case of new investment. Because of the specific and even distribution of the feed material to the whole depth of the chipping area, the present invention makes it possible to build chipping machines of large dimensions with deep chipping areas. This means that machines that are not so large deliver equal throughput performance, so that the costs for foundations, electrical connections, and delivery systems are reduced.
In one particular embodiment, the present invention has rotating impact surfaces that in the case of a similarly rotating circular blade set can advantageously be driven independently of this. This means that the feed material is not only deflected through 90xc2x0 at the impact surfaces, but is simultaneously accelerated in a radial direction, as well.
Configuring the impact surfaces as rotationally symmetrical bodies such as circles, annular rings, or truncated cones prevents excessive wear on the impact surfaces, since the working areas of the impact surfaces are minimized in this way and it promotes orderly flow conditions within the chipping area.
Whereas in the case of impact surfaces with enclosed surfaces, the feed material that is entering axially crosses the trajectories of the deflected feed material, thereby causing collisions that have an adverse effect on orderly flow conditions within the chipping area, one especially advantageous embodiment of the present invention makes crossing-free guidance of the feed material possible. According, to this, because of a central opening, the impact surfaces are in the form of an annular ring. The annular surface of these impact surfaces can also be inclined, which results in a hollow truncated cone. In this way, the present invention is adapted to beater wheels in which the beater-wheel seat extends into the chipping area. This embodiment also entails the advantage that the feed material does not strike the impact surface at a right angle and is thereby deflected into a radial direction that reduces wear.
The fact that the impact surfaces can be displaced in the axial direction makes it possible to optimize the impact surfaces in order to achieve even wear on the chipping tools. Proceeding from the basic adjustment with the diameter of the impact surface being {fraction (1/10)} to ⅓ of the diameter of the beater wheel or the impact surfaces being arranged so as to be spaced apart at a constant distance form each other, optimization takes place in that a) the wear on the chipping tools at specific positions prior to operation is determined; b) the machine is operated for a specific amount of time; c) the wear on the chipping tools at the places identified in a) is determined; the diameter and/or spacing of the impact surfaces is varied in the event that the wear on the chipping tools is not constant at the locations identified in a); the steps a) to d) are repeated until such time as the wear on the chipping tools is constant at the locations identified in a). The advantage of such a procedure is that all borderline conditions are taking into account, as are such influences that would be too complex for a theoretical investigation.
The rectangular configuration of the entry opening that, even in the case of a comparatively low height, extends to the width of the overall inside diameter of the beater wheel ensures that the feed material strikes all the impact surfaces in equal quantities, so that it is evenly distributed to the depth of the chipping area. In addition, the flow of air generated for wind sifting can be used for pneumatic delivery of the feed material without any significant deflection, so that its energy can be exploited to the fullest possible extent.
By using guide panels, the width of the entry opening can be divided in several segments that preferably correspond to the axial material tracks.